JPS6478206A - Detecting method for defocusing quantity - Google Patents

Abstract

PURPOSE:To detect the defocusing quantity of a photographic lens with high accuracy by calculating the difference between object information when auxiliary light is used and object information when not, calculating the defocusing quantity from the object information at the time of the auxiliary light and performing correction with a specific correcting quantity which cancels the movement quantity of an image formation position. CONSTITUTION:An image of an object is formed by a focus lens group 20A and formed on an image pickup surface through a master lens group 20D. Then when the photoelectric output waveform of a CCD line sensor 32 to the object image deviates, the defocusing is detected from the quantity and direction of the deviation. The object information obtained from a sensor for focus detection when the auxiliary light is used, is mixed information containing the information obtained when the circumferential light is used, so the object information at the time of the use of only the circumferential light is also detected and subtracted from the mixed information to perform the correction by using the specific correcting value for canceling the movement quantity of the image formation position of the photographic lens, thereby finding the defocusing quantity at the time of the use of the auxiliary light. Consequently, the defocusing quantity of the photographic lens is detected with high accuracy regardless of the quantity of the circumferential light.